A problem concerned with electrically powered portable grinders is to lead away the heat generated during operation so as to protect the electric motor and other components of the grinder from being exposed to detrimentally high temperatures.
The common way to accomplish temperature control in electric grinders and similar power tools is to incorporate in the power tool a fan and suitable air circulation passages in the tool housing for ducting cooling air past the hottest areas of the tool.
A problem inherent in these fan cooled power tools is that they circulate the ambient air at the working site which in many cases is heavily contaminated with dust and debris from the working process. This is a particularly serious problem at grinders, because the ambient air at the working site is always more or less contaminated with aggressive particles. All these air born particles not only cause a clogging up of the air circulation passages in the tool housing with an impaired cooling effect as a result, but act as a blasting means wearing down the material of the tool housing and, even worse, wearing down the windings of the electric motor, thereby causing short circuiting and/or current interruption, i.e. interruption of an ongoing working process. Dust particles entering the tool will also cause a severe wear on the motor and spindle bearings.
Even though fan cooled power tools normally are provided with some sort of filter devices to prevent dust penetration into the tool housing and motor, these filter devices are very limited in size not to cause increased outer dimensions of the tool housing. This means that such a small size filter device has a very small air penetration area resulting in that they get clogged up very quickly and the risk for reduced cooling and motor overheating is great. To avoid this, short service intervals are required for exchange or cleaning of the filter device. Still, dust penetrates into the tool motor and bearings and causes a limited service life of the power tool.
Another problem relating to fan cooled electric power tools is the space demand for the cooling fan. It is in fact undesirable to make room for a cooling fan inside a portable power tool since this type of tools is required to have as small as possible outer dimensions for comfortable handling.